A high speed page width ink jet printer has recently been developed by the present applicant. This typically employs in the order of 51, 200 ink jet nozzles to print on A4 size paper to provide photographic quality image printing at 1,600 dpi. In order to achieve this nozzle density, the nozzles are fabricated by integrating MEMS-CMOS technology and in this context reference may be made to International Patent Application No.PCT/AU00/00338 lodged by the present Applicant and entitled "Thermal Actuator".
These high speed page width ink jet printers produce an image on a sheet by causing a thermal bend actuator arm to move relative to a substrate by forming the actuating arm in part from an electrically resistive material and by applying a current to the arm to effect movement of the arm. The arm is connected to a paddle so that upon movement of the arm the paddle is moved to eject a droplet of ink onto the sheet. In order to eject the droplet of ink the paddle extends into a nozzle chamber which has a nozzle aperture, and movement of the paddle causes the droplet to be ejected from the nozzle aperture. The actuating arm is fixed at one end and when current is applied to the arm the arm is caused to bend to, in turn, move the paddle so as to eject the droplet from the nozzle aperture. In order for the paddle to move properly, so as to eject the droplet, the actuating arm is required to bend upwardly and generally pivot around the fixed end of the arm. Bending of the arm is caused by the application of an electrical current to the arm which causes an elongation of part of the arm relative to another part of the arm. To ensure that the actuating arm bends properly it is necessary to control bending modes of the arm which may result in improper movement of the paddle which may effect the ejection of a droplet from the nozzle chamber. For example, the elongation of one part of the arm relative to the other can cause the arm, rather than to bend upwardly as required, to curl up at the sides forming a general dish shaped configuration, or bend into a sinusoidal configuration or other curved configuration. These bending modes may result in improper movement of the paddle which, as noted above, may effect the manner in which a droplet is ejected from the nozzle chamber.